1. Field of the Invention
The present invention relates to a vibration driven motor for generating a travelling vibration wave in a vibration member upon application of a voltage to an electro-mechanical energy conversion element, and causing relative movement between the vibration member and a member contacting it by frictional driving and, more particularly, to a high-output type vibration driven motor.
2. Related Background Art
In a conventional vibration driven motor, especially in a high-output type vibration driven motor, a thin annular piezo-electric element is fixed on the rear surface of an annular vibration member substrate formed of, e.g., stainless steel, and a super hard material containing tungsten carbide and cobalt is spray-coated on the front surface of the substrate and is polished to form a hard sliding surface, thus constituting a vibration member. On the other hand, a member contacting the vibration member is constituted by fixing, on a support member of, e.g., an aluminum alloy, a slide member having a reinforced composite resin layer prepared by filling and blending a reinforcement material such as a carbon fiber in a thermoplastic resin having a glass transition point of 100.degree. C. or higher, e.g., heat-resistant resins such as polyimide (PI), polyamide imide (PAI), polyether imide (PEI), polyether ether ketone (PEEK), polyether sulfone (PES), polyarylate (PAR), polysulfone (PSF), liquid-crystal aromatic polyester (LCP), or the like, or nonthermoplastic aromatic polyimide (PI). The vibration member and the contact member move relative to each other by frictional driving caused by a travelling vibration wave generated in the vibration member.
The relative movement between the contact member and the vibration member may be attained while either of these members is fixed or movable. In the following description of the present specification, however, the vibration member is fixed in position, and the contact member is movable for the sake of simplicity. Therefore, the contact member will be referred to as a "movable member" hereinafter.
In the conventional vibration driven motor, the slide member containing as a base material a thermoplastic resin having a glass transition point of 100.degree. C. or higher or a nonthermoplastic aromatic polyimide resin is used as the reinforced composite resin layer forming a portion of the movable member for the following reasons. That is, these heat-resistant resins have small temperature dependency as a material physical property, do no suffer from a torque-down phenomenon due to softened resins caused by a temperature rise upon driving of the motor, and can stabilize performance precision of the motor.
A reinforcement material such as a carbon fiber is filled in the resin materials for the following reasons. First, the property of the slide surface of the movable member is always stabilized with respect to the slide surface of the vibration member, which surface is formed of the super hard material containing, e.g., tungsten carbide and cobalt, and sufficient wear resistance in a driving operation for a long period of time can be assured. Second, the material physical property values such as elasticity, hardness, and the like of the slide member are increased to improve the performance (e.g., an output) of the motor. Third, the heat conductivity of the slide member is increased to improve the performance (e.g., efficiency) of the motor.
As described above, since the reinforced composite resin prepared by filling a carbon fiber in a heat-resistant thermoplastic resin having a glass transition point of 100.degree. C. or higher, or a nonthermoplastic polyimide resin is used in the slide member for providing the slide surface of the movable member in the vibration driven motor, the performance and precision of the motor can be stabilized against a temperature rise upon driving of the motor, and the wear resistance against the super hard material forming the slide surface of the vibration member is sufficient even after a driving operation for a long period of time. Furthermore, motor performance such as output efficiency can exhibit a high value.
However, when the slide surface of a composite resin layer of a movable member, which layer contained a heat-resistant thermoplastic resin or nonthermoplastic aromatic polyimide resin, and was reinforced by filling a carbon fiber, was actually brought into contact with a hard slide surface, formed of a super hard material, of a vibration member under pressure, and a driving operation was started under rated operation conditions of, e.g., 4 kg.multidot.cm and 100 rpm, torque nonuniformity of about 5% occurred with respect to the rated torque value, and further improvements were demanded.
Furthermore, when the driving operation was performed for as long as 1,000 hours under the rated relatively high-output conditions, a wear of 3 .mu.m or more was observed even on the carbon fiber-reinforced composite resin layer, and further improvements of frictional materials were demanded.
Moreover, since the spray-coated friction surface having a film thickness of 50 to 100 .mu.m and formed of tungsten carbide and cobalt had relatively poor heat conductivity, thermal radiation performance to the movable member constituted by the composite resin layer and the support member was poor, and it caused a temperature rise of the vibration member.